Long question, gas cap & check engine light

[Catcoach]

Sorry about the length but you have to hear the whole story. MH is a 98 Winnebago with the Ford 460, Banks Power system. Left Colorado on a trip to South carolina, everything is fine out of the driveway, then 10 miles from home the check engine light came on, stayed on all the way to SC. Someplace along the way I left the gas cap at a gas station, so while in SC bought a new gas cap at Checker. Check engine light on all the way home until we come to Monarch Pass, as we are going up the pass we come around a corner to encounter another motor home blocking the road. Quick stop, now the engine won't start. Back down to an off the highway safe area, that was fun with no power, limited brakes etc. One hour later still can't get the engine to start, acts like vapor lock but it is fuel injected. Finally try taking off the gas cap, unbelievable sucking sound. Now the engine starts fine, and the check engine light is off, so away we go, get to the top of the pass, stop to check things out etc, and decide to put the gas cap back on. By the time we get halfway down the pass I can tell that that the engine is starving for fuel, won't accelerate etc, check engine light back on,stop at the bottom of the pass, pull the gas cap, another unbelievable sucking sound from the fuel system. Leave gas cap off drive home, some 90 miles no problems, and the check engine light stays off. Assumed I had a bad gas cap, went to my local Ford dealer bought new gas cap and you guessed it same problem. Rig drives great without the gas cap, put the gas cap on and the check engine light comes on and soon we experience fuel starvation.
Local Ford dealer has no idea, so I am going to the brain trust, that's all of you. Thoughts, suggestions, or should i just drive without the gas cap?
Thanks

[GreaTOne65]

Gas caps are supposed to be designed to allow air in (vented), but keep gas in. Driving with out the cap is not a very good idea. What I would do, is check the cap and determine where the cap is suposed to let air into the tank. Has to be something obvious, if not drill the cap under the cover, don't want it to leak water into the tank, so it will breath.

[wa8yxm]

The first check engine light was because you forgot the gas cap (Cue TV commercial, for On-Star, Kelly Rippa of Regis Live, calls in because her check engine light is on,, The On-Star rep reads the telemetry and asks "Did you just buy gas")

The second one was because the new cap was defective.

Get a new gas cap, Make sure it's for a modern vehicle and properly check vented.

[OneRVer]

I am just thinking out loud here but I would go to the truck division of ford and buy a gas cap for the F-450. I do know you do need some vacuum in your tank and when there is not enough vacuum then you engine light will come on. I am thinking the caps you bought were not designed for the volume size of your gas tank. Ps, one way to reset your Engine Light is to pull the battery cable for about 30 seconds and then put back on. Good Luck and let us know the final results.

[bluepill]

A few thoughts:

1. Without reading codes, there is no way to be sure that the Check Light is coming on because of the venting problem. The code(s) might point directly to a tank venting problem, or indirectly (such as a misfire due to lack of fuel), or something unrelated (just coincidence)

2. Different tank designs require different cap parameters. Many non-factory caps are not calibrated correctly. Get the correct one from Winnebago to be sure. Otherwise you can end up chasing your tail. Been there, done that.

["007"]

Check the vent tube thats tied to the fuel fill pipe.
Some times they drop below fill pipe and gas will back up into vent tube and you lose the vent air.
The check engine light will come on in this event.

[tderonne]

There's no evaporative monitor on the F53 chassis until at LEAST the 2006 model year. Not sure if the 2006 has one, but I know none of the 460's or the V10 through the 2004 model year have an evap monitor.

So, the gas cap was NOT the source of the check engine light for sure.

[Catcoach]

Thanks for all of the great suggestions, Think I will go with another new gas cap, this time from Winnebago ( last one came from Ford), and check the vent tube. This is why this forum is fantastic

[JimM68]

put a code reader on the diagnostic port...

Silly to throw parts and money at something when it's smart enough to tell you what's broke, should you simply ask.

I imagine both the light and the symptom have to do with a problem with the evaporative emission control system. I wouldn't think to guess what, just ask the computer.

[subford]

On your year of the F53, one of the codes that you could get and more than likely it is the one you are getting is that the engine is running lean and the O2 sensor is giving a lean code.


Another code and not as likely is that the positive displacement fuel gear pump is drawing too much current. If the fuel pump is bogging down trying to to pump against the vacuum that it has created it may draw too much current and the voltage will drop. The computer will get this information from the fuel pump monitor pin #8 that checks voltage levels on the fuel pump power feed wire.

The vent tube will not cause this problem as it is only used as you fill the tank.

The vapor vent roll over valve on top of the tank going to the Evaporative Emission (EVAP) System will not give a code either as the only tie to the computer is the on and off solenoid valve on the tube from the charcoal canister.

[mpaton]

Posts #7 and #10 contain real factual information you can use. Here's some more facts.

Both your Banks exhaust and the almost universal 10% ethanol fuel you can't avoid using will cause your 460 to run more lean than Ford intended.

Many will tell you that your Oxygen sensor will compensate for this, and it would if this engine ran it Closed Loop fueling mode. However Ford programmed your engine to almost never run in Closed Loop mode, and so you aren't getting any compensation for the leaner fuel mixtures.

Any 460 engine owner should have an OBD-1 code reader and know how to use it. This is because the computer can have fault codes set, but will NOT set the Check Engine light for those codes. So don't wait for a light before you go looking for faults the computer knows about.

When you provoke your light into going on, there WILL be a code. After the light is off there may or may not still be a code.

And now the opinion; If I were you I would find out what that code was. You have reduced margins already on running lean, and these engines are tough, but repairs can also be expensive.

[OneRVer]

[QUOTE=mpaton;1005205]
Many will tell you that your Oxygen sensor will compensate for this, and it would if this engine ran it Closed Loop fueling mode. However Ford programmed your engine to almost never run in Closed Loop mode, and so you aren't getting any compensation for the leaner fuel mixtures.
QUOTE]

Why would Ford install an Oxygen Sensor and then use it as an Open Loop and what would determine when the Oxygen Sensor is used in a closed Loop?

[wa8yxm]

Interesting info on the closed/open loop thing.. I know I'm not a Ford fan.. I guess this is PART of the reason why.. Alas, the CEO of GM ticked me off big time too.

[She and I]

I think I would change the fuel filter..and check fuel pump pressure..Also I think your chassis is a 1997 because the V10 came out in 1998 on most Rv's not the 460.
Hope you find the reason
Richard